The present invention relates to a printing process for forming a printed image on a printing medium by an electrostatic ink jet method using an oil-based ink, more specifically, the present invention relates to an ink jet printing process and a printing apparatus, where an image is formed by an ink jet method and a printed matter is prepared by contact-transferring the image onto a printing medium and where very high-quality printed image and high-speed printing can be attained.
The printing process for forming a printed image on a printing medium based on image data signals includes an electrophotographic method, a sublimation-type or melting-type heat-transfer method and an ink jet method.
The electrophotographic method requires a process of forming an electrostatic latent image on a photoreceptor drum through electrification and exposure and therefore, suffers from complicated system and expensive apparatus.
The heat-transfer method uses an ink ribbon and therefore, despite its inexpensive apparatus, suffers from high running cost and treatment of a waste material.
The ink jet method performs the printing directly on a printing medium by ejecting an ink only on a desired image area using an inexpensive apparatus and therefore, ensures efficient use of a coloring agent and low running cost.
With respect to the method for applying the ink jet technology to printing system, for example, JP-A-10-286939 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) discloses a process for additionally printing variable numbers, marks or the like on the same printing paper using the ink jet system by providing an ink jet printing apparatus to a rotary printing press.
The printing of image information is preferably in a level as high as comparable to the photographic image, however, conventional ink technologies of pressure-ejecting an aqueous or organic solvent-type ink containing a dye or pigment as a coloring agent is disadvantageous in that since a droplet containing a large amount of a solvent is ejected, unless expensive exclusive paper is used, the printed image blurs.
Accordingly, in the case of performing the printing on a normal printing paper, a plastic sheet as a non-absorptive medium, or the like, a high-quality printed image cannot be obtained.
As one of the ink jet technologies, a method of heat-melting an ink which is solid at an ordinary temperature, and jetting out the obtained liquid ink to form an image is known. When this ink is used, blurring of the printed image may be reduced, however, because of high viscosity of the ink at the ejection, a fine droplet cannot be jetted out and the obtained individual dot images are large in both the area and the thickness, as a result, a high-precision image cannot be formed.
The present invention has been made to solve the above-describe problems.
That is, an object of the present invention is to provide an ink jet printing process where an inexpensive apparatus and a simple method can be used, the ink can be ejected at exact positions with extremely high precision, a high-precision image can be in turn formed, and a printed matter having a clear and high-quality image can be printed.
Another object of the present invention is to provide a printing apparatus for realizing the process.
Other objects and effects of the present invention will become apparent from the following description.
The above-described objects of the present invention have been achieved by providing the following processes and apparatuses.
(1) A printing process for preparing a printed matter comprising:
forming an image on the surface of an image carrier by an ink jet method comprising ejecting an oil-based ink using electrostatic field based on signals of image data; and
contact-transferring the image formed on said image carrier onto a printing medium to prepare a printed matter.
(2) The ink jet printing process according to item (1) above, wherein said oil-based ink comprises:
a nonaqueous solvent having an electric resistivity of 109 xcexa9cm or more and a dielectric constant of 3.5 or less; and
a component dispersed in said nonaqueous solvent, which comprises at least colored particles.
(3) The ink jet printing process according to item (1) or (2) above, further comprises adjusting a surface temperature of said image carrier to the range of from 30 to 40xc2x0 C. at the time of forming an image on said image carrier.
(4) The ink jet printing process according to any one of items (1) to (3) above, further comprising fixing the image contact-transferred onto the printing medium.
(5) A printing apparatus comprising:
ink jet drawing unit which ejects an oil-based ink from an ejection head using an electrostatic field based on signals of image data to form an image on an image carrier; and
image transfer member which contact-transfers the image formed on said image carrier onto a printing medium to obtain a printed matter.
(6) The printing apparatus according to item (5) above, wherein said oil-based ink comprises:
a nonaqueous solvent having an electric resistivity of 109 xcexa9cm or more and a dielectric constant of 3.5 or less; and
a component dispersed in said nonaqueous solvent, which comprises at least colored particles.
(7) The printing apparatus according to items (5) or (6) above, wherein said image carrier is a rotary body comprising a drum or an endless belt.
(8) The printing apparatus according to any one of items (5) to (7) above, wherein said image carrier has elasticity.
(9) The printing apparatus according to any one of items (5) to (8) above, further comprising a temperature-controlling member which adjusts a surface temperature of said image carrier to the range from 30 to 40xc2x0 C. at the time of ejecting the ink on said image carrier from said ink jet drawing unit.
(10) The printing apparatus according to any one of items (5) to (9) above, further comprising a cleaning member which cleans said image carrier.
(11) The printing apparatus according to any one of items (5) to (10) above, further comprising an image fixing member which fixes the image contact-transferred onto said printing medium.
(12) The printing apparatus according to item (11) above, wherein said image fixing member has a heating member comprising at least one of a heat roller, an infrared lamp, a halogen lamp and a xenon lamp.
(13) The printing apparatus according to item (12) above, wherein said heating member is disposed and/or controlled to gradually elevate a temperature of said printing medium at the time of fixing said image.
(14) The printing apparatus according to any one of items (7) to (13) above, wherein said rotary body is rotatable to perform main scanning at the time of drawing an image on said image carrier.
(15) The printing apparatus according to item (14) above, wherein said ejection head comprises a single channel head or a multi-channel head and is movable in a direction parallel to the axis of said rotary body to perform sub-scanning.
(16) The printing apparatus according to item (14) above, wherein said ejection head comprises a full line head having almost the same length as a width of said rotary body in the axis direction.
(17) The printing apparatus according to any one of items (5) to (16) above, wherein said ink jet drawing unit further has an ink supply member which supplies said oil-based ink to said ejection head.
(18) The printing apparatus according to item (17) above, further comprising an ink recovery member which recovers said oil-based ink from said ejection head.
(19) The printing apparatus according to any one of items (5) to (18) above, wherein said ink jet drawing unit further has an ink tank for storing said oil-based ink and a stirring member which stirs said oil-based ink in said ink tank.
(20) The printing apparatus according to any one of items (5) to (19) above, wherein said ink jet drawing unit has an ink temperature-controlling member which controls the temperature of said oil-based ink in at least one of an ink tank for storing said oil-based ink and an ink passage.
(21) The printing apparatus according to any one of items (5) to (20) above, wherein said ink jet drawing unit has an ink concentration-controlling member which controls the concentration of said oil-based ink.
(22) The printing apparatus according to any one of items (5) to (21) above, further comprising at least a pair of capstan rollers which allows said printing medium to travel while being interposed and held therebetween to perform the transfer.
(23) The printing apparatus according to any one of items (5) to (22) above, further comprising a cleaning member which removes dusts present on the surface of said printing medium at least one of before and during the transfer onto said printing medium.
(24) The printing apparatus according to any one of items (5) to (23) above, further comprising a cleaning member which cleans said ejection head.
As understood from these constructions, the present invention has a feature that an image is formed on the surface of an image carrier by an ink jet method of ejecting an oil-based ink using an electrostatic field and the image is contact-transferred onto a printing medium to prepare a printed matter.
The image carrier has a lubricant surface, as described later, on a drum or the like capable of being worked and disposed with high mechanical precision and at the same time, the distance from the head can be precisely adjusted, so that the ink can be ejected at exact positions with extremely high precision and therefore, a high-precision image can be formed.
The image is formed on a printing medium through contract-transfer from the image carrier, so that the contact pressure, contact temperature and the like of the ink at the transfer onto the printing medium can be controlled to appropriate values and therefore, the retentivity of image transferred onto the printing medium can be elevated. When the transferred image is subjected to a fixing step, the retentivity of image can be more improved.
The ink jet process according to the present invention is described in PCT Publication WO93/11866. In this ink jet process, an ink having high resistance obtained by dispersing at least colored particles in an insulating solvent is used, a strong electric field is allowed to act on this ink at the ejection position to form an agglomerate of colored particles at the ejection position, and the agglomerate is ejected from the ejection position using electrostatic means. As such, the colored particles are ejected as an agglomerate formed to a high concentration and the ink droplet contains only a small amount of solvent, as a result, a high-density clear image free of blurring is formed on the surface of a drawing drum. xx
In this ink jet process, the size of the ink droplet ejected is determined by the size of the distal end of the ejecting electrode or the conditions in forming the electric field. Therefore, when a small ejection electrode and appropriate electric field-forming conditions are used, a small ink droplet can be obtained without reducing the ejection nozzle size or slit width.
In other words, the present invention provides an ink jet printing process where a fine image can be controlled without causing any problem of ink clogging in the head and a printed matter having a clear and high-quality image can be printed.